1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and more particularly to a liquid ejection head and an image forming apparatus which eject ink droplets from nozzles by driving liquid ejection devices, such as piezoelectric elements.
2. Description of the Related Art
In recent years, image forming apparatuses based on an inkjet system (i.e., inkjet recording apparatuses), which record desired images on recording media by ejecting ink from heads having a plurality of nozzles (i.e., liquid ejection heads), have come to be widely used. In these heads, each of the nozzles is provided with a liquid ejection device, which is typically a piezoelectric element or a heating element, and ink droplets are ejected from the nozzles by selectively driving the liquid ejection devices.
There are the inkjet recording apparatuses in which a selector circuit for selecting the liquid ejection device to which a drive signal is to be applied, is constituted separately from the head, and the selector circuit is connected to the head through a flexible printed circuit (FPC). However, it is technically difficult to reduce the wiring pitch in the flexible printed circuits, and hence there are limitations on the increase in the nozzle density in the head that can be achieved. Furthermore, there is also a problem in that high-density flexible printed circuits are expensive.
In view of the above-described problems, Japanese Patent Application Publication No. 9-314833, for example, discloses a head in which, rather than using the flexible printed circuit, thin film transistor (TFT) elements of equal number to the piezoelectric elements are arranged on a side wall of a reservoir corresponding to a common flow channel (i.e., on a drive substrate). In this head, however, the wires arranged on the drive substrate start from the face on which the thin film transistor elements are arranged, and stretch along another face perpendicular to the former face, and hence complicated manufacturing steps are required and reliability declines. Moreover, the wires of the drive substrate are connected directly to the piezoelectric element terminals, and this composition is technically very difficult. Furthermore, in order to ensure reliability, it is necessary to increase the size of the head by increasing the thickness of the wires, or the like, and this leads to problems of additional costs.
Japanese Patent Application Publication No. 9-314831 discloses a head in which an integrated circuit (IC) chip and wires are arranged on a covering member that covers three faces of the main body of the head. In this head, however, both the signal wires and the control signal wires arranged on the covering member are connected to the same face of the IC chip, and there is no prospect of reducing the installation surface area on the cover member. Moreover, it is technically difficult to connect the cover member to the three faces of the main body of the head. Furthermore, Japanese Patent Application Publication No. 9-314831 discloses that a low-density connection method using soldering, or the like, is used for connecting the electric terminals on the cover member with the electric terminals on the main body of the head; however, this is not suitable for high-density connections. Consequently, similarly to Japanese Patent Application Publication No. 9-314833, there are problems in that this leads to increased size of the head and increased costs.
In order to ensure the reliability of the connections, it is necessary to reduce the high-density connection sections (from the IC to the piezoelectric element side). It is hence desirable to install the IC on the head, also from the viewpoint of reducing the number of components; however, this incurs increased size of the head in order to ensure sufficient installation surface area.